The inventive concept relates to a semiconductor buffer structure, a semiconductor device including the semiconductor buffer structure, and/or a method of manufacturing the semiconductor device using the semiconductor buffer structure.
As a substrate for forming a nitride-based semiconductor device, a sapphire substrate is often used. However, sapphire substrates are typically expensive and have a high hardness, they are typically not suitable for chip manufacturing. Sapphire substrates also generally have low electric conductivity. In the epitaxial growth of a large-size sapphire substrate, the substrate is bent at high temperature due to the low heat conductivity of sapphire. Accordingly, it is difficult to manufacture a large-area sapphire substrate. To overcome such limitations, nitride-based semiconductor devices using a silicon substrate instead of a sapphire substrate have been developed. The silicon substrate, due to having a higher heat conductivity than the sapphire substrate, does not need to be bent as much as a sapphire substrate, even at the high temperatures required for growing nitride thin films. Accordingly, growth of a large-size thin film may be possible with a silicon substrate.
However, when a nitride thin film is grown on a silicon substrate, the dislocation density increases due to a difference in lattice constant between the silicon substrate and the thin film, and cracks may be generated due to tensile stress caused by a difference in thermal expansion coefficient between the silicon substrate and the thin film. Thus, various buffer layer structures for growing a nitride thin film layer capable of avoiding cracks while having high crystallinity on a silicon substrate have been proposed.
A buffer layer offsets the lattice constant and thermal expansion coefficient differences between the silicon substrate and a target layer to be formed thereon, for example, a nitride semiconductor thin film. To grow the nitride semiconductor thin film, such as GaN, on the silicon substrate, an AIN nucleation layer is typically grown on the silicon substrate, and the GaN thin film is grown using the resulting substrate of AlN on GaN as a pseudo-substrate. To reduce dislocations and cracks in the GaN thin film, a buffer layer is typically formed on the nucleation layer.
When a GaN thin film is used for a Light Emitting Diode (LED) or a power device, the GaN thin film has to be grown to have low dislocation for performance improvement and to receive compressive stress for crack prevention. However, as the GaN thin film grows, stress evolves to tensile stress because of dislocation bending, and if there are too many dislocations, a crack is generated during the growth of the GaN thin film. Thus, the main objectives of using a buffer layer are stress control and removal of dislocations from the buffer layer. To this end, a buffer layer structure that has a lattice constant between the AIN nucleation layer and the GaN thin film, and in which the lattice constant changes in the form of a step grade or a continuous grade, may be proposed.